The present invention is directed to a method for converting pulse-shaped, highly structured analog signals into trigger pulses with an electronic circuit whereby the trigger pulses are locked for a specific time, which is referred to as dead time, and is also directed to an electrical circuit operating in accordance with the method.
In various measurements, trigger pulses that are highly precise in terms of time, are required. Trigger pulses are derived from the signal rise of analog signals. For example, position signals of the blades of turbine engines, that are highly precise in terms of time, are required. Optical probes are utilized for this purpose. The blades pass through an illumination beam prepared by the probe, and analog signals are acquired from the light reflected from the end face of the blades. The irregular surface structure of the end faces of the blades can lead to fractured analog signals with which fades down to zero are possible.
For converting the analog signals into trigger pulses according to the prior art, the beginning of a trigger pulse is derived with a trigger circuit when the analog signal exceeds a specific threshold, the trigger pulse being in turn ended when the threshold is downwardly transgressed. Given highly fractured analog signals that comprise fades down to zero, misfirings occur given such a method since an individual analog signal is not converted into a long trigger pulse but into a number of shorter sub-pulses.
In order to prevent multiple triggerings, the trigger circuit given this known method, is locked for a specific time, which is referred to as dead time, after every triggering that ensues, whereby the dead time is manually set to a fixed value.
What thereby has a disadvantageous effect is that, in order to avoid pulse failures, the dead time must be selected shorter than the shortest time spacing of the analog signals to be anticipated. Therefore given decreasing signal frequencies and analog signals that become correspondingly longer, these are no longer completely covered by the dead time and multiple triggerings occur.